Engine analyzer for detecting temperature with self-healing transducer and circuits



1956 J. E. LINDBERG, JR 2,759,172

ENGINE ANALYZER FOR DETECTING TEMPERATURE WITH SELF- HEALING TRANSDUCER AND CIRCUITS Filed Oct. 28, 1953 i 3 Sheets-Sheet l ,IIlIII/IIIII/f L III/l INVENTOR. John E. Llnclber' ,Jn BY M (0w ATTORNEK g- 1956 J E. LINDBERG, JR 2,759,172

ENGINE ANALYZER FOR DETECTING TEMPERATURE WITH SELF-HEALING TRANSDUCER AND CIRCUITS Filed Oct. 28, 1953 3 Sheets-Sheet 2 INVENTOR.

JOHN E. LIIVOBERQJR.

0TB}, a M w 57 ATTORNEY g- 1956 J. E. LINDBERG, JR 2,759,172

ENGINE ANALYZER FOR DETECTING TEMPERATURE WITH SELF-HEALING TRANSDUCER AND cmcurrs Filed Oct. 28, 1953 3 Sheets-Sheet 3 xI y! L 7 INVENTOR.

JOHN E. Ll/VDBE/FG, JR.

QMC W ATTORNEY United States Patent O ENGINE ANALYZER FOR DETECTING TEMPERA- TURE WITH SELF-HEALING TRANSDUCER AND CIRCUITS John E. Lindberg, Jr., Lafayette, Calif.

Application October 28, 1953, Serial No. 388,832

15 Claims. (Cl. 340-227) This invention relates to an engine analyzer for detecting changes in temperatures or pressure.

One deficiency with engine analyzers heretofore in use was in failing to detect and indicate critical changes in temperature, such as excessive temperature in any one of the combustion chambers or such as fires occurring in the engine. The present invention solves that problem with the aid of a novel transducer, in which temperature or pressure changes are utilized to produce changes in an electric circuit. The engine analyzer, utilizing this transducer can be used for temperature sensing and fire detecting.

The analyzer of this invention also is applicable to other types of maximizing systems including control systems for controlling the fuel flow on jet aircraft, so that all combustion chamber temperatures are continuously surveyed and the highest temperature is automatically maintained as near as possible to the safe critical temperature of the combustion chamber, that is as high a temperature as the combustion chamber can safely be operated without exceeding the temperature above which the component partswould fail. It is desirable to operate at as high a temperature as is safely possible, because the power and efii ciency of a power plant increases with increased operating temperature.

This application is a continuation-in-part of application Serial No. 318,291, filed November 1, 1952. The present invention relates particularly to an analyzer employing a transducer with a self-healing interior coating on its interior surface, while a companion application Serial No. 388,831, filed October 28, 1953, relates to the broader aspects.

The novel transducer is very sensitive to a predeter; mined critical temperature or pressure. It is characterizedby its extreme simplicity of operation and of manufacture, by its freedom from delicate, easily injured parts, by its great versatility, and by its ability to replace complicated and expensive apparatus heretofore in use. As a'result, it has solved important problems in systems such as engine analyzers where indication of or control by a critical temperature or pressure is needed, of which engine analyzer temperature sensing as a fire-detection warning will serve as an example.

Fire-detecting systems heretofore in use have employed moving parts, electronic circuits, or other delicate and expensive equipment which has been prone to get out of order readily and has also been difiicult to repair. The expense of the sensitive elements themselves and'of the systems as a whole has prevented wide use of fire-detecting devices and has confined them heretofore to places where they were absolutely essential. Many fire-detecting devices were seriously affected by vibration or by a change in attitude, so that they were useless in such applications as warning systems in aircraft.

The single point type detectors commonly used in the past sufier from the additional problem that they can only detect excessive temperature at a pre-selected single point, which commonly turned out not tube the pointat 'ice which fire occurred. In an attempt to overcome this difiiculty, systems were built incorporating many single point detectors distributed through the zone to be protected' and wired together. This proved unsatisfactory due to complexity, wiring failures, and sensitivity loss (because each additional detector lowered the circuit sensitivity), and even with the many detectors it was a common occurrence for there to be no detec or in the right point to detect the fire.

To overcome these problems, attempts have been made todevelop a satisfactory continuous type fire detector so that the complexities would be eliminated and the continuous type transducer element could readily be distributed through the zone to be protected.

However, many, if not most of the continuous type fire-detecting systems heretofore in use would not react at the same temperature each time; the triggering temperature depended on the length of detector element exposed to the higher temperature. For example, with some fire detectors a temperature of about 400 F. acting over a one-foot length of a sensitive element had the same effect as a 750 F. temperature acting over a few inches of the same sensing element. Not only in this instance, but in other instances, prior art fire-detecting devices were likely to give false alarms so that the user was never sure whether anything significant had been detected or not.

My invention is a transducer of the continuous element type so designed that it will show an immediate large increase in resistance when any point or points along the entire length of the element reach the pre-selected critical temperature. The setting is not affected by the length of the exposed element.

The present invention has solved these problems by pro viding a novel type of transducer in which the change of state of liquid to a gas is used to interrupt an electric current. The boiling point of a liquid depends solely on the composition of the liquid, the pressure, and the temperature. By deciding upon one specific liquid, and by holding the pressure constant, the reaction will always occur at the identical temperature. Similarly, if the temperature is held constant, the reaction will always occur at the same pressure.

When an electrically conductive liquid changes to a gas, the increase in resistance is tremendous. Even a single fraction of an inch of gas interrupting a long tube full of liquid, will cause substantially complete interruption of current flow. For example, a liquid may have a resistance of 300,000 ohms across a one-foot path. If even a single bubble of vapor breaks the continuity of this path, and if there is no possibility of shorting around this gas bubble, the resistance becomes substantially infinite, many millions of ohms. This very sharp break enables accurate detection of a precise temperature. By connecting the transducer in parallel with a warning light such as a neon flash-tube or with a relay that operates a'warning light or an audible signal, the instant that a single vapor bubble appears at any point along the transducer or in any one of a series of transducers, all the voltage will'pass through the warning relay or warning light and give a signal. That is one of the principles of my new transducer and. of its application to a fire or critical-temperature or critical-pressure detecting system.

One advantage of my invention is that anincrease beyond the critical temperature at any point along the transducer will have the same effect as an increase-over a wide area. Any one transducer, once filled with liquid, will respond throughout at the same temperature-pressure level. A series of identical transducers will all respond in the same Way. When desired, by using different pressures'with the same liquids or by using. different liquids, in different transducer elements, a series of difiierent transducers may be made so that each transducer can be responsive to a different critical temperature and still give the same signal.

The invention has other advantages. The transducer is filled with liquid; there are no void spaces. Any expansion occurs in the container itself. Therefore, it is unaffected by vibration or by a change in attitude or by being subjected to very low temperatures below the freezing point of the liquid. No electronic system or moving parts are required. The individual elements may be made about the same size as relatively small diameter wire; a series of them may be joined together to give whatever length is desired, and they may be placed anywhere they are desired. There is nothing to get out of order, and

the entire system is very easily tested to make sure that it is operating correctly.

All of these and other objects and advantages of the invention will appear from the following description of some preferred embodiments thereof and some uses therefor,

for the use of the transducer in a fire-detecting system is but one use to which this versatile element is adapted. The details of structure which are shown in the drawings and description are given in order to comply with 35 U. S. C. 112 and to make it possible for anyone to .con-

struct the device. equivalents may be substituted. For that reason, the claims are not intended to be limited narrowly by the mention of the details in the specification.

In the drawings:

Fig. 1 is an enlarged isometric view of a transducer incorporating the principles of my invention.

Fig. 2 is a greatly enlarged isometric view in section taken along the line 22 of Fig. 1 and broken ofl to conserve space.

Fig. 3 is an isometric view greatly enlarged and partially cut away taken along the line 33 of Fig. 1.

Fig. 4 is a greatly enlarged longitudinal view in section, taken along the path indicated by the line 4-4 in Fig. 2 and broken in the middle to conserve space.

These details may be changed, and

Fig. 5 is a diagrammatic view showing the change in cross section which takes place with changes of internal pressure and showing the shape toward which the tube tends to change under internal pressure, so as to take care of expansion of the fluid.

Fig. 6 is a view similar to Fig. 2 showing a modified form of the invention in which the transducer is held in a protecting shell.

Fig. 7 is a view in section similar to Fig. 4 of a modified form of the invention in which a Bourdon tube is employed to take care of the expansion of the fluid. The view is broken in the middle to conserve space, and a partially uncurled position, assumed upon an increase in internal pressure is shown in dotted lines.

Fig. 8 is a circuit diagram showing a fire-detecting system employing the transducer of this application.

Fig. 9 is a circuit diagram showing a series of transducers joined together in a fire-detecting system.

Fig. 10 is a circuit diagram showing how one of my transducer elements may be used to give a reading of the maximum temperature present over a given area.

Fig. 11 is a circuit diagram showing the use of alternating current in a maximum-temperature detecting system.

Fig. 12 is a diagrammatic view showing how a series of transducers may be used in a circuit to control the fuel feed for a jet aircraft engine.

Fig. 13 is a view similar to Fig. 12 showing how a single transducer may be used for the same purpose.

Fig. 14 is a diagrammatic view of an arrangement,

of Fig. 11, showing only the circuit portion to the right of points 16, 16.

The transducer As stated previously, the invention provides a novel type of transducer in which the change of state of an electrically conductive liquid is used to interrupt an electric current. Many examples could be given of suitable transducers, and it would be impossible to show herein all the feasible types. However, a few examples are given, and it is believed that they serve to illustrate the principle.

The transducer 20 as shown in Figs. 1 to 5 includes a flattened tube 21. The tube 21 is made from metal, because metal is less liable to breakage, because metal can be bent into shape, and because of an insulating inner coating 22 with a self-healing property that will be described in a moment. A basic consideration is that the inside wall of the transducer tube should be non-conductive and insulate the metal tube 21 from the liquid inside the tube. If a coating is placed on the tube 21, by spraying enamel on a metal sheet before the tube is formed, care must be taken to see that the coating does not break and cause short circuits. Also, the coating must be able to withstand the temperatures with which the transducer is to be used. In the present invention the material for the tube 21 is one that forms an electrically insulating film 22 when properly treated by any of several already wellknown techniques. Metals with this property include aluminum, tantalum, :columbium and many others which form adherent insulating anodic films.

Similarly, the electrically conductive liquid 23 which fills the tube 21 is of a known type which may be used to form such film, but which will not react with the metal of the tube or the thin film after the formation of the film. For example, boric acid and other weak acids may be used with aluminum, while sulfuric acid, hydrochloric acid, and other strong acids may be used with tantalum.

The coating 22 is a very good insulator, even though it is very thin, and it performs the very important function of insulating the metal of the tube 21 from the liquid 23, thereby preventing short circuits. Where there is no such insulating layer 22 the formation of a gas bubble would not interrupt the electric flow, because current could bypass it through the metal to the liquid on the other side of the bubble. The coating 22 formed by the reaction of the liquid 23 with the metal 21 assures a uniform selfhealing coating that will not break readily, and if it breaks it will be instantly and automatically replaced. In order to prevent the coating 22 from breaking down while the transducer 20 is conducting current, the body 21 should always be kept biased electrically positive with respect to the electrodes.

The primary advantages of the metal-liquid combination are: (1) that it gets all the advantages in strength, ductility, and heat resistance which may be obtained from metal tubes; (2) it is relatively fool-proof so far as short circuits within the tube 21 are concerned, due to its insulation self-healing property; and (3) the insulation formed can withstand a very high temperature, so that the fire detector can continue to operate undamaged after extended exposure to high temperatures met in a severe fire.

One further remark should be made about the choice of material for the tube 21. The tube 21 should be able to withstand the maximum temperature to which the transducer 20 may be submitted. This temperature may be many times hotter than the temperature which the transducer 20 is to indicate, because, when a fire occurs, the device should indicate as soon as possible that there is a fire, before the fire reaches its greatest heat. In most cases it is desirable to have a transducer 2!} that will not have to be replaced after the fire, but will still be in good shape after the fire has been put out. Two choices are available here. The tube 21 may be made from a metal which can withstand these temperatures. However, this isinot' completely necessary, for (as Fig. 6 shows); the metal tube 21 may be jacketed in a protecting metal sheath or shell 24. The shell 24 may. be made of steel or some other metal which is well able to Withstand high temperatures. It will still conduct the necessary heat energy and it will serve to retain the tube in its general shape without damage, up to very. high temperatures. It should also be able to conduct electricity to the wall of the tube 21.

A further remark may also be made about the liquid 23 which is used inside the transducer. In addition to its electrical properties and its desirable coating-forming property, it is of course essential that the liquid boil at the proper temperature. The boiling point, however, may be regulated to a considerable degree by the absolute pressure with which the liquid is retained inside the tube 21, whether this pressure be above or below atmospheric. This well-known phenomenon makes it possible to provide with great exactness for a wide range of critical temperatures, limited only by the structural limits of the transducer.

The transducer 20 has a pair of spaced-apartelectrodes 25, 26, which may be, and preferably are in most cases, located at opposite ends of the tube 21. (However, they need not be; see Figs. 7 and l0.) The metal of the electrodes 25, 26 should not form a coating when in contact with whatever electrolyte 23 is used. The electrodes 25, 26 are insulated from the tube 21 by members 27, 23, which may be made from ceramic or from some other type of insulating material. The members 27, 28 may be sealed to the electrodes 25, 26, and to the tube 21 to prevent leakage.

The sensitivity of the transducer 20 is increased by making the tube 21 as small in cross-sectional area as is otherwise convenient. The smaller the tube, the less heat energy that is required to actuate it at the predetermined temperature. This is because of two things: the smaller amount of liquid to be heated and the. smaller amount of liquid whose state must be changed in order to interrupt the column of liquid. With a large tube, considerable liquid would have to be heated in order to interrupt the path, and during the heating some of the adjacent liquid would have to be heated, because of the conduction and convection within the liquid. With a small tube, very little liquid has to be heated before complete discontinuity is caused by vapor. The limits of sizeof the tube 21 depend upon the materials available. Quite satisfactory operation has been obtained with the tube 21, whose greater diameter is approximately of an inch and whose lesser diameter is approximately of inch, but other dimensions, of course, may be used to practice this invention. The length of the tube 21 is not a factor in this phase of operation. The tube 21 may be a few inches long or a number of feet long. Or they may be joined in series, as illustrated in Fig. 9. Preferably the tube will be elongated and be uniform in cross-section, at least between the electrodes, so that all parts are equally responsive, and it will be a temperature maximizing transducer.

When the liquid inside the transducer becomes heated, the pressure upon the transducer tube walls is increased. Also, if the liquid freezes, the pressure may increase. Therefore, some way is preferably provided to accommodate some changes in the volume of the fluid, and inthe device shown in Figs. l through 5 this is accomplished by using a flattened metal tube. Fig. 5 shows diagrammatically that such a tube 21, when subjected to high internal pressure, tends to change its shape by becoming more nearly circular. The dotted line'circle indicates the shape in which the same circuit of walls encloses'the greatest volume and is therefore the shape Where the pressure is lowest. However, the tube 21 does not actually reach that shape, but instead assumes the shape indicated by the dotted oval 31. Any change in shape from the flattened cross section toward a circular cross section in- 6 creases the volume insidethe tube walls and therefore relieves-the fluid-pressure.

Another way of handling this problem isto house'the liquid 23 in a Bourdon tube 32. To simplify this draw ing the coating 22: is shown as a single line here. As Fig. 7 shows, an increase in pressure tends touncurl or straighten out-the curved portion 33 of the Bourdon tube and thereby allow for expansion in volumewhile maintaining the pressure at a substantially constant level.

Other ways of handling increases in fluid pressure inside the tube may be used. For example one end of the tube may be provided with a diaphragm, bellows or piston arrangement Summarizing the operationsof the transducer itself: a current flow is maintained between the two electrodes 25 and 26 through the liquid 23. When the transducer 20 is subjected to heat at any portion along its length, that heatis conducted through the walls of the tube 21 and through the thin coating 22 to the liquid 23 and raises its temperature. If the temperature be excessive, eventually the liquid 23 at some point along the length of the tube 21 will reach the critical temperature-pressure figure, and-it will boil. When just enough liquid, at any point, changes its state to a-gas to cause a discontinuity in the liquid, the electric current between the electrodes 25 and 26-will be interrupted, andno current will flow. Since the inside wall of the tube 21 is either non-conductive or is covered with a non-conductive coating 22, there will be no short circuit around the gas gap in-the liquid, and the current will remain interrupted until the temperature goes down, andthen current will again flow between the electrodes 25 and 26.

The increase in internal pressure that is generally. caused by an increase in temperature may be compensated for as by having walls of the tube expandand thereby maintain a near constant pressure, or the increase in pressure may itself be used in combination with the increase in temperature to mark the critical figure at some predetermined temperature-pressure condition.

The device may also be used for indicating-the attainment of a critical pressure in the same manner. The temperature may either be kept constant or be permitted to vary somewhat with the change in pressure. In either event, the vaporization of the liquid will interruptthe electric current flow through the transducer.

Circuits showing applications of the transducer Several circuits to which the transducer are shown in the drawings. The circuit shown in Fig. 8 places the transducer 20' in an electric circuit having a power source 35 and a resistance 36 in series witli'the transducer 20. A condenser 37 and a neon flash bulb 38 are placed in parallel'with each other and with the transducer 29. So long as current flows through thetransducer 20, there is a voltage drop through the resista'nce36, and this resistance is so chosen that the voltage available to the neon bulb 38 is less than its breakdown voltage; so no. current flows through it normally.

To preventsa breakdown of the coating 22* and'assure self-healing properties, the tube 21 is biased positively,- by a battery 39, shown here with its negative side connected to an electrode 25 and its positive side at ground, with the wall 21 also grounded. The battery39 has a larger voltage than the battery 3'5, so that a positive bias will at 'all times, duringoperation, be maintained across the-film 22, thereby preserving it or restoring it ifiit is damaged.

When the transducer'20 becomes heated and gas forms at any point in it, the current flow through the transducer 20 is interrupted. This means that no current flows through the resistor 36; so'there is no voltage drop there. This, in turn, causes a charge to build up on the condenser 37 until finally a voltage is reached there which isequal to or greater than the breakdown voltage ofthe neon tube 38. Then, the neon tube will discharge-the condenser 37, emitting a warning flash-as it does so, and so longas no may be applied current flows through the transducer 20, the condenser 37 will alternately become charged by the power source 35 and discharged by the neon lamp 38. When and if all the 'ance 36, and the neon bulb 38 will cease flashing.

Instead of a neon bulb 38, a relay or other warning signal may be used, preferably in series with a neon bulb or other device that draws current only when the transducer 20 gases. The relay, if used, may operate a fire extinguishing system (in aircraft a C system, in industrial or home use a sprinkler system) or other remedial device. Also, a relay in series with the transducer may replace the bulb.

Fig. 9 shows another very simple but very practical circuit, employing a series of transducers 20. Again the source 35 of direct current is connected through a resistor 36 to the series of transducers 20, and the condenser 37 and neon flasher 38 are in parallel with the transducers 20. The transducers 20 are linked together by wires and may be disposed in any pattern anywhere; for example, they may encircle an aircraft engine. All of the transducers 211 except a portion of the first and last ones are shown as beyond a fire wall 40. Their walls are all grounded with a battery 39 keeping the tube 21 positive with respect to the battery 35. Instead of being grounded, the connection may be direct, and there may be a separate battery 39 for each transducer 20.

Fig. 9 also shows a test device by which the transducer 20 may be checked periodically. A heating coil 41 surrounds the last tube 21, and a switch 42 is provided to control the current through the coil 41. Whenever the heater 41 is turned on, it soon reaches a temperature above the boiling point of the liquid 23 inside the transducer 20. When the liquid 23 boils, there is a gap, a discontinuity, in the liquid, the current flow between the electrodes 25 and 26 ceases, and the neon flash bulb 38 is lighted. This indicates to the operator that the device is working satisfactorily, and the switch 42 may then be turned off. By placing the heater 41 on the last transducer 20, the flashing of the neon tube means that the entire circuit is working in proper order.

It may also be added that the condenser 37 could be omitted and the circuits would still work, though less well. Also, alternating current may be used in place of direct current, and then the condenser 37 should be left out. If A. C. is used, the battery 39 should have greater voltage than the A. C. supply peak voltage.

Alternating current circuit Fig. 11 shows how the transducer 20 of the present application can be used with alternating current. The use of the metal tube 21 with a coating 22 that insulates the metal from the electrically conductive liquid makes this possible, and the self-healing nature of the coating 22 increases the practicability of this circuit.

The transducer 20 has its electrodes 25, 26 connected across the secondary 70 of a transformer 71, as a source of A. C. current, with the neon flasher lamp 3% in parallel with the transducer 20. No condenser 37 is used here as it would short circuit the A. C.

The transformer 70 has another secondary winding 72, with more turns than the secondary 70, so that it has a higher voltage. A rectifier 73 is placed in series with the secondary 72 and with the tube wall 21 so that the metal wall 21 is kept positive with respect to the electrodes 25, 26 at all times, the D. C. potential there being greater than the maximum A. C. potential to the electrodes.

Secondary 70 provides an alternating voltage source greater than the trigger voltage of the neon tube 38, or other warning device that is to be used; therefore when 'heat causes the conducting fluid in 20 to boil, and a bubble interrupts the current flow between electrodes 25 and 26, the warning light or device will give an intermittent warning flash or-signal at the frequency of the alternating current source. Fig. 16 shows a relay 74 in series with the 8 transducer 20, instead of the parallel circuit of Fig. 11. The relay 74 may operate bulb 38 or other device.

A hunting circuit using the transducer to give a reading of the maximum temperature over the full length of the transducer The transducer 50 of Fig. 10 is similar to the transducer 20 except that one electrode 25 is not placed in the end of the tube but, rather, through the side near one end, and an expansion chamber 51 is provided for fluid 23 beyond this electride 25. The expansion chamber is bounded by a bellows 52 by which the pressure on the liquid 23 may beincreased or decreased.

It is obvious that an increase in pressure on the liquid 23 will raise its boiling point, while a decrease in pressure will lower its boiling point. Therefore, by proper operation of the bellows 52 the temperature at which the liquid 23 boils may be made to fall at practically any point. It is also apparent that once the constitution of the liquid 23 is known and its physical constants determined, the boiling point depends solely on the pressure. A pressure gauge 53 connected to the expansion chamber 51 may therefore be made to read in terms of the boiling temperature of the liquid; that is, when the circuit is interrupted, the indicator on the gauge, if correctly calibrated, will show what the boiling temperature is. .Of course, the

gauge does not read in temperatures except with regard' to the moment at which the fluid is boiling and therefore interrupting the current. By this means it is possible to use the transducer 50 as a thermometer to indicate with great exactness what is the maximum temperature over the area to which the transducer 50 is exposed.

The transducer 54 when connected in the circuit shown in Fig. 10, may be used as a hunting device to continually hunt for the maximum temperature. For this purpose a second, entirely independent expansion chamber 54 is provided to hold another fluid 55. The bellows 56 for the expansion chamber 54 is joined with the bellows 52 of the expansion chamber 51 by 'a-rod 57. Movement of the rod is opposed normally by a spring 58. As shown in Fig. 10, this connection is such that an expansion of the fluid (e. g., through an increase in temperature) will bring about a reduction of pressure in the expansion chamber 51 and therefore will tend to cause the fluid 23 to boil.

A source 60 of electric current is connected in series with the transducer 23, and a resistance type heater 61 placed in series with this source 60 and the electrodes 25 and 26 may be used to heat the expansion chamber 54. So long as the fluid 23 does not boil, current will pass through the resistance 61 and will heat the fluid 55 thereby expanding it. This expansion will, through the rod 57, cause an expansion of the bellows 52 thereby reducing the pressure on the fluid 23. The heating will be kept up and the fluid 55 will get hotter, causing further expansion of its bellows 56 and a further reduction of the pressure on the liquid 23 until the combination of the reduced pressure on the liquid 23 and the maximum ambient temperature to which any point along the transducer 50 is exposed, reach the critical value at which at least a portion of the liquid 23 boils. When it does boil, the gauge 53 will indicate the temperature at which it is boiling. Or a gauge 63 may be attached to the expansion chamber 55 to read in terms of the temperature at which the liquid 23 boils, or a strain gauge may be connected to the rod 57, or other indicating means ma be employed.

When the liquid 23 boils, not only is the temperature indicated but also the circuit is broken and therefore the heater 61 cools oif permitting the liquid 55 to cool until such time as the liquid 23 drops below the boiling point and then the heater 54 is started again. This continuous interaction between the liquids 23 and 55 means that the circuit of Fig; 10 will continually seek out the Use of the transducer in a control circuit Fig. 12 shows diagrammatically how the transducer 20 may be used in a control circuit for feeding fuel to a jet aircraft engine 80. Here it is desired to maintain the engine temperature very near a maximum figure, but not to exceed that maximum figure. The higher the temperature, the greater the power and efiiciency of the engine 80, but if it gets too hot, the engine 80 will be damaged. Accordingly, a series of transducers 20 are placed around the engine 80 (e. g., one at each combustionchamber 81), with the boiling point of the liquid 23 inside them being set for the desired maximum temperature and below the temperature which would be harmful to the engine 80. When the temperature does increase beyond the desired amount, at any point in any of the transducers 24), the circuit is broken.

The. transducers 20 are in series with a power source 82 and with a resistance 83. A variable resistor 84 is placed in series with the transducers 20 and a relay 85 is placed in parallel with them, so that the circuit here is generally similar to that of Fig. 9, with a relay substituted for the neon flash bulb. Preferably, the relay 85' draws no current, except when the circuit is broken somewhere in one of the transducers 20.

The relay 85 operates a switch 86 that controls a second electric circuit having a power source 87. This circuit operates a motor 88 that controls a valve 89 in the fuel supply line '90. Normally a spring 91 causes the valve 89 to tend toward its fully open position, too wide an opening being prevented by the stop 92. Whenever the relay 85 is actuated, the motor 88 begins to oppose the spring 91 and to reduce the fuel passing through the valve 89.

As soon as the temperature in the combustion chamber 81' cools off and the gas in the transducer 20 condenses, current flows through the transducers 20, and then the relay 85 is opened, the reduction of flow of fuel is stopped, and the spring 91 causes the fuel flow to. increase.

In this instance the flow is ordinarily (that is so long as current flows through the transducers 20) set at an amount which is the maximum practicable flow. Then the engine 80 will naturally tend up toward the maxi.- mum temperature and will be maintained near that temperature by the control action of the transducers 20 and the transducer-controlled relay 81.

The variable resistor 84 makes it possible to vary the current. through the transducers 20 and thereby raise the temperature, of the liquid therein, so as to increase the sensitivity of the device and in some cases to trigger the reaction at a, somewhat different level of ambient temperature.

Fig. 13 shows a single long transducer 95 substituted for the series of shorttransducers 20, with the. same result; Here, also, a bellows arrangement 96 on aprojecting end 9'1 of the transducer 95, makes it possible to regulate the critical temperature by regulating the pressure-on the fluid. In addition, a fluid pressure gauge 53 makes it possible to read the maximum temperature in the system at the time the liquid first boils, especially when the gauge 53 is calibrated to give a direct temperature reading.

Although the transducers in Figs. 12 and 13 are shown adjacent the combustion chambers 81, they may be placed in oracross the flame area inside the chambers for. more direct control; A series-connected relay, as in Fig. 16,

may be used instead of the parallel-connected relay. Figs. 12 and 13 are only representative of what may be done; the transducer would normally be incorporated; as part of an overall power-control system to control the throttle of fuel flow or to vary the turbine exhaust area, to obtain maximum efficiency without exceeding the critical temperature.

Engine analyzer for detecting location of circuit breaks Another type of engine-analyzer. circuit is represented in Figs. 14 and 15. The transducer elements, it will.:be understood, will be disposed as in Fig. 12 or Fig. 13; The present circuits are used to analyze the actuating circuit break by locating its exact position, which is the position of the maximum temperature along the lineof the transducer.

Here, a source of alternating current is used with a single transducer 20- (Fig. 14) or a series of them (Fig. 15). They are disposed as are the transducers 20 and 95 in Figs. 12 and 13, but the completearrangement shown in those figures is not illustrated, for the sake of simplicity. The outer metal wall 21 of thetransducer 20 is grounded at 101, as is one side of the A. C. power. source 100.

The maximum temperature has already been obtained by the use of the Fig. 13 analyzer. its location will now be obtained by another application of the engine analyzer. This is supplemental to the other functions of the engine analyzer shown in my Patent No. 2,518,427 of August 8, 1950. The present setup may be placed into and .out of connection with the analyzer cathode ray indicator tube of that patent by a simple switch, preferably incorporated as a part of the engine analyzer condition selector switch.

A potentiometer 102 is placed across the transducer electrodes 25, 26, and a cathode ray tube 103 is also connected across the same electrodes. Only two facing plates 104, 105 of the tube 103 need be used, though a four-plate tube can be used and is normallyused in the engine analyzer.

When a bubble'B breaks the column of fluid in a tube 20,.the location of the bubble B is to be determined, i. e. the distances x and y which make up the two segments of liquid in the tube and add up to itsfull length L. The effect thenis to make of the two liquid columns two condensers Cx and Cy, whose values may be determined.

One method of determining x and y begins by. ad justing the arm 106 of the potentiometer 102 to bring the light beam in the tube 103 to the center 107 of the cathode ray tube screen 108. The position-of the arm 106 then corresponds to the position of the bubble B, and can be calibrated to give the distances x and y, for the resistances R1, and R2 are then in the same proportion as x and y, i. e. R1:R2::x:y.

The second method is to make R1=R2 at. all times, as fixed components. Then the position of the light beam is calibrated on the screen 108. Then if the beamis at 109, it will represent the position of the bubble B. The screen 108 is calibrated by locating two points a and H on the screen 108 corresponding to the positionof the beam when the bubble B is at positions a, b, respectively at each end of the transducer 20. Then the distance L between a and b corresponds to the distance L between a and b and the ratio of x to y' corresponds to the ratio of x to y.

It should be borne in mind that the impedances R1 and R2 are impedances and that condensers are even pref: erable to resistors, as this would then make the circuit a pure capacitance bridge, because the result of the bubble B'is to make the two columns of liquid in the tube into condensers Cx and Cy, separated by the bubble B.

The Fig. 15 circuit difiers principally from the Fig. 14 circuit in having aplurality of transducers 20. inplace of the transducer 95. The length L is therefor made up of a series of segments L1, L2, L3 etc., in each transducer 20. The distance between successive transducers is immaterial for there is no capacitance in the connections between them. The transducers may all be the same length, or some may be longer than others, but the analyzer will show the location of the bubble B in terms of total transducer length. The operation is otherwise identical with that of Fig. 14. If either circuit is used in the Fig. 12 arrangement, the analyzer will locate the hottest combustion chamber.

In place of the tube 103, a voltmeter can he used in the analyzer, or the circuit shown could be replaced by a capacitance measuring device to give the values of Cx and Cy or their ratio.

The fact that the value of either capacitance Cx or Cy may be obtained of course makes it possible to use the transducer 20 as a condenser, employing the self-healing coating as a dielectric between the liquid and the metal outer wall. Since the location of the bubble B can be found by a capacitance measuring device, it is obvious that the existence of the bubble B can be determined in the same manner, by the change in capacitance indicated. It will be apparent that the same transducer may be used to detect the presence of fire, etc. by indicating the change in capacitance instead of the change in resistance.

From the foregoing it will be seen that a great variety of transducers may be made according to'the principles of the above invention. It will also be seen that a great variety of fire-detection systems may be made with various differences in circuitry and that difierent types of warning systems and control devices may be actuated by the transducer. It will also be apparent that, in addition to fire detection or temperature control, the transducer 20 and the circuits to which it is adapted may be used for other temperature, or pressure, or temperatureand-pressure control. Since temperature may be created by various forms of energy which have themselves been caused by other effects, a transducer may be used with suitable apparatus to control other effects indirectly.

It will be understood that in any of these transducers the change of state could also be from a liquid to a solid and vice versa, so long as an appreciable change in resistance results from the change in state.

The transducer has no moving parts, is very simple to manufacture in quantity, it is able to withstand considerable shock or other damage and lends itself to a versatility of operations that is not equalled by any analogous device known heretofore. It makes it feasible to install fire-Warning systems in private homes and to keep them inconspicuous or even concealed beneath the wall and to give automatic alarm indications and to set off controls.

Obviously, instead of indicating the attainment of a high temperature or low pressure at a desired point by breaking an electric circuit, the same transducer may be used to indicate when the last point along the transducer has attained a selected low temperature or, alternately, the highest pressure, over a given transducer path. This may be determined by normally having the fluid at least partly in the gaseous state and having it complete a normally broken circuit when all the gas becomes a liquid. In this case the warning device or indicator will normally be in series with the transducer.

A transducer with its walls fairly flexible can well be used to indicate maximum pressure, for local pressure along the transducer will then be able to readily deflect the wall 21 of the continuous transducer and thereby directly afiect the pressure on the fluid 23. The ability of the transducer fluid to expand in volume should then be limited, so that the maximum local pressure will not flatten out the tube only locally (see Fig. 5), but will transmit the maximum pressure undiminished throughout the fluid 23, making only a slight local effect, as distinguished from the general efiect.

Another use of the transducer is in such devices as those shown in the Warner patent, No. 2,648,726, wherein a liquid current-modulating medium is used in such transducer applications as phonograph pickups. Then, the body would not have to be made from plastic or other insulating materials, but could be made from metal. The applications of this invention are not limited to-when liquid boils.

To those skilled in the art to which this invention relates, many changes in construction and widely difiering embodiments and applications of the invention will suggest themselves Without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A transducer, including in combination a metal container; an electrically conductive liquid in said container, said liquid and metal being of the types that react to form a thin, electrically-insulating film that prevents further reaction between them; and a pair of electrodes insulated from said container and spaced apart from each other by the liquid, so that the electrical connection between them depends upon the liquid, and when said liquid gases, the current flow will be interrupted, said electrodes being of a material that does not react with said liquid to form an insulating film.

2. A transducer, including in combination a metal container; an electrically conductive liquid in said container, said liquid and metal being of the types that react to form .a thin, electrically-insulating film that prevents further reaction between them; and a pair of electrodes insulated from said container and spaced apart from each other by the liquid, so that the electrical connection between them depends upon the liquid and said transducer outputdepends upon variation in resistance of the liquid current path, said electrodes being of a material that does not react with said liquid to form an insulating film.

3. A transducer, including in combination a closed metal container having a self-healing inner insulating coating; an electrically conductive liquid in said container; and a pair of electrodes for passing current through said liquid so that when said liquid gases, the current flow will be interrupted.

4. A. transducer, comprising a narrow tube of filmforming metal; a film-forming electrolyte filling said tube; and a pair of non-film-forming electrodes sealed in the opposite ends of said tube and insulated from said tube.

5. The transducer of claim 4 in Which there is an electrical connection to the Wall of said tube.

6. The transducer of claim 4 in which the metal tube is positively biased with respect to the electrodes.

7. The transducer of claim 3 in which said tube is jacketed in a shell of metal that can withstand high temperatures.

8. A fire-detection apparatus, comprising a flattened narrow tube of a film-forming metal; a film-forming electrolyte filling said tube; a pair of electrodes sealed in the opposite ends of said tube and insulated from said tube; a source of current at substantial voltage but insufiicient power to heat said electrolyteto the boiling point; a resistance in series with said electrodes; biasing means of higher voltage than said current source connected between said metal tube wall and one electrode; a condenser in parallel with said electrodes; and a signal means in parallel with said electrodes, said signal being responsive to said voltage when the current through said electrolyte is blocked by the boiling of a portion thereof and otherwise being unresponsive to the voltage.

9. A transducer, including in combination a closed metal container having a self-healing inner insulating coating; an electrically conductive liquid in said container; and a pair of electrodes for passing current through said liquidso that variation of the resistance in said liquid controls the output of the transducer.

10. A transducer, comprising a flattened narrow tube of film-forming metal; a film-forming electrolyte filling said tube; and a pair of non-fiirn-forming electrodes sealed in the opposite ends of said tube and insulated from said tube.

11. A fire-detection apparatus, comprising a flattened narrow tube of a film-forming metal; a film-forming electrolyte filling said tube; a pair of electrodes sealed in the opposite ends of said tube and insulated from said tube; a source of current at substantial voltage but insuflicient power to heat said electrolyte to the boiling point; a resistance in series with said electrodes; biasing means of higher voltage than said current source connected between said metal tube wall and one electrode; and a signal means responsive to said voltage when the current through said electrolyte is blocked by the boiling of a portion thereof and otherwise being unresponsive to the voltage.

12. A transducer, comprising a narrow tube of anodizable metal; an anodizing electrolyte filling said tube; and a pair of non-anodizing electrodes sealed in the opposite ends of said tube and insulated from said tube.

13. A transducer, including in combination a metal container chosen from the group of anodizable metals,

consisting of aluminum, tantalum, columbium, and the like; an acidic liquid able to anodize the selected metal in said container, and a pair of non-anodizable electrodes insulated from said container and spaced apart from each other by the liquid, so that the electrical connection between them depends upon the liquid.

14. A transducer, including in combination a closed aluminum container; a weak anodizing liquid acid in said container; and a pair of electrodes for passing current through said liquid.

15. A transducer, comprising a flattened narrow tube of tantalum; a strong tantalum-anodizing acid in liquid form, filling said tube; and a pair of non-film-forming electrodes sealed in the opposite ends of said tube and insulated from said tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,976,700 Lilienfeld Oct. 9, 1934 2,117,874 Clark May 17, 1938 2,346,836 Grooms Apr. 18, 1944 

